On-chip mode division multiplexing (MDM) has been heavily researched over decades, which transmits multiple channels in one shared multimode bus waveguide to enhance transmission capacity. A number of MDM devices have been developed, including multiplexers/demultiplexers (MUX/DEMUX), mode order filters and mode order converters. The mode order converters are used to convert high order modes to transverse electric fundamental mode (TE0) first before processing, and the high order mode converting process is one major challenge of on-chip MDM. Accordingly, it is desired to realize high order mode converters in compact sizes.